src/net/http/client.go - go - Git at Google

 // Copyright 2009 The Go Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style
 // license that can be found in the LICENSE file.

 // HTTP client. See RFC 2616.
 //
 // This is the high-level Client interface.
 // The low-level implementation is in transport.go.

 package http

 import (
 	"encoding/base64"
 	"errors"
 	"fmt"
 	"io"
 	"io/ioutil"
 	"log"
 	"net/url"
 	"strings"
 	"sync"
 	"sync/atomic"
 	"time"
 )

 // A Client is an HTTP client. Its zero value (DefaultClient) is a
 // usable client that uses DefaultTransport.
 //
 // The Client's Transport typically has internal state (cached TCP
 // connections), so Clients should be reused instead of created as
 // needed. Clients are safe for concurrent use by multiple goroutines.
 //
 // A Client is higher-level than a RoundTripper (such as Transport)
 // and additionally handles HTTP details such as cookies and
 // redirects.
 type Client struct {
 	// Transport specifies the mechanism by which individual
 	// HTTP requests are made.
 	// If nil, DefaultTransport is used.
 	Transport RoundTripper

 	// CheckRedirect specifies the policy for handling redirects.
 	// If CheckRedirect is not nil, the client calls it before
 	// following an HTTP redirect. The arguments req and via are
 	// the upcoming request and the requests made already, oldest
 	// first. If CheckRedirect returns an error, the Client's Get
 	// method returns both the previous Response and
 	// CheckRedirect's error (wrapped in a url.Error) instead of
 	// issuing the Request req.
 	//
 	// If CheckRedirect is nil, the Client uses its default policy,
 	// which is to stop after 10 consecutive requests.
 	CheckRedirect func(req *Request, via []*Request) error

 	// Jar specifies the cookie jar.
 	// If Jar is nil, cookies are not sent in requests and ignored
 	// in responses.
 	Jar CookieJar

 	// Timeout specifies a time limit for requests made by this
 	// Client. The timeout includes connection time, any
 	// redirects, and reading the response body. The timer remains
 	// running after Get, Head, Post, or Do return and will
 	// interrupt reading of the Response.Body.
 	//
 	// A Timeout of zero means no timeout.
 	//
 	// The Client's Transport must support the CancelRequest
 	// method or Client will return errors when attempting to make
 	// a request with Get, Head, Post, or Do. Client's default
 	// Transport (DefaultTransport) supports CancelRequest.
 	Timeout time.Duration
 }

 // DefaultClient is the default Client and is used by Get, Head, and Post.
 var DefaultClient = &Client{}

 // RoundTripper is an interface representing the ability to execute a
 // single HTTP transaction, obtaining the Response for a given Request.
 //
 // A RoundTripper must be safe for concurrent use by multiple
 // goroutines.
 type RoundTripper interface {
 	// RoundTrip executes a single HTTP transaction, returning
 	// the Response for the request req.  RoundTrip should not
 	// attempt to interpret the response.  In particular,
 	// RoundTrip must return err == nil if it obtained a response,
 	// regardless of the response's HTTP status code.  A non-nil
 	// err should be reserved for failure to obtain a response.
 	// Similarly, RoundTrip should not attempt to handle
 	// higher-level protocol details such as redirects,
 	// authentication, or cookies.
 	//
 	// RoundTrip should not modify the request, except for
 	// consuming and closing the Body, including on errors. The
 	// request's URL and Header fields are guaranteed to be
 	// initialized.
 	RoundTrip(*Request) (*Response, error)
 }

 // Given a string of the form "host", "host:port", or "[ipv6::address]:port",
 // return true if the string includes a port.
 func hasPort(s string) bool { return strings.LastIndex(s, ":") > strings.LastIndex(s, "]") }

 // refererForURL returns a referer without any authentication info or
 // an empty string if lastReq scheme is https and newReq scheme is http.
 func refererForURL(lastReq, newReq *url.URL) string {
 	// https://tools.ietf.org/html/rfc7231#section-5.5.2
 	//   "Clients SHOULD NOT include a Referer header field in a
 	//    (non-secure) HTTP request if the referring page was
 	//    transferred with a secure protocol."
 	if lastReq.Scheme == "https" && newReq.Scheme == "http" {
 		return ""
 	}
 	referer := lastReq.String()
 	if lastReq.User != nil {
 		// This is not very efficient, but is the best we can
 		// do without:
 		// - introducing a new method on URL
 		// - creating a race condition
 		// - copying the URL struct manually, which would cause
 		//   maintenance problems down the line
 		auth := lastReq.User.String() + "@"
 		referer = strings.Replace(referer, auth, "", 1)
 	}
 	return referer
 }

 // Used in Send to implement io.ReadCloser by bundling together the
 // bufio.Reader through which we read the response, and the underlying
 // network connection.
 type readClose struct {
 	io.Reader
 	io.Closer
 }

 func (c *Client) send(req *Request) (*Response, error) {
 	if c.Jar != nil {
 		for _, cookie := range c.Jar.Cookies(req.URL) {
 			req.AddCookie(cookie)
 		}
 	}
 	resp, err := send(req, c.transport())
 	if err != nil {
 		return nil, err
 	}
 	if c.Jar != nil {
 		if rc := resp.Cookies(); len(rc) > 0 {
 			c.Jar.SetCookies(req.URL, rc)
 		}
 	}
 	return resp, err
 }

 // Do sends an HTTP request and returns an HTTP response, following
 // policy (e.g. redirects, cookies, auth) as configured on the client.
 //
 // An error is returned if caused by client policy (such as
 // CheckRedirect), or if there was an HTTP protocol error.
 // A non-2xx response doesn't cause an error.
 //
 // When err is nil, resp always contains a non-nil resp.Body.
 //
 // Callers should close resp.Body when done reading from it. If
 // resp.Body is not closed, the Client's underlying RoundTripper
 // (typically Transport) may not be able to re-use a persistent TCP
 // connection to the server for a subsequent "keep-alive" request.
 //
 // The request Body, if non-nil, will be closed by the underlying
 // Transport, even on errors.
 //
 // Generally Get, Post, or PostForm will be used instead of Do.
 func (c *Client) Do(req *Request) (resp *Response, err error) {
 	if req.Method == "GET" || req.Method == "HEAD" {
 		return c.doFollowingRedirects(req, shouldRedirectGet)
 	}
 	if req.Method == "POST" || req.Method == "PUT" {
 		return c.doFollowingRedirects(req, shouldRedirectPost)
 	}
 	return c.send(req)
 }

 func (c *Client) transport() RoundTripper {
 	if c.Transport != nil {
 		return c.Transport
 	}
 	return DefaultTransport
 }

 // send issues an HTTP request.
 // Caller should close resp.Body when done reading from it.
 func send(req *Request, t RoundTripper) (resp *Response, err error) {
 	if t == nil {
 		req.closeBody()
 		return nil, errors.New("http: no Client.Transport or DefaultTransport")
 	}

 	if req.URL == nil {
 		req.closeBody()
 		return nil, errors.New("http: nil Request.URL")
 	}

 	if req.RequestURI != "" {
 		req.closeBody()
 		return nil, errors.New("http: Request.RequestURI can't be set in client requests.")
 	}

 	// Most the callers of send (Get, Post, et al) don't need
 	// Headers, leaving it uninitialized.  We guarantee to the
 	// Transport that this has been initialized, though.
 	if req.Header == nil {
 		req.Header = make(Header)
 	}

 	if u := req.URL.User; u != nil {
 		username := u.Username()
 		password, _ := u.Password()
 		req.Header.Set("Authorization", "Basic "+basicAuth(username, password))
 	}
 	resp, err = t.RoundTrip(req)
 	if err != nil {
 		if resp != nil {
 			log.Printf("RoundTripper returned a response & error; ignoring response")
 		}
 		return nil, err
 	}
 	return resp, nil
 }

 // See 2 (end of page 4) http://www.ietf.org/rfc/rfc2617.txt
 // "To receive authorization, the client sends the userid and password,
 // separated by a single colon (":") character, within a base64
 // encoded string in the credentials."
 // It is not meant to be urlencoded.
 func basicAuth(username, password string) string {
 	auth := username + ":" + password
 	return base64.StdEncoding.EncodeToString([]byte(auth))
 }

 // True if the specified HTTP status code is one for which the Get utility should
 // automatically redirect.
 func shouldRedirectGet(statusCode int) bool {
 	switch statusCode {
 	case StatusMovedPermanently, StatusFound, StatusSeeOther, StatusTemporaryRedirect:
 		return true
 	}
 	return false
 }

 // True if the specified HTTP status code is one for which the Post utility should
 // automatically redirect.
 func shouldRedirectPost(statusCode int) bool {
 	switch statusCode {
 	case StatusFound, StatusSeeOther:
 		return true
 	}
 	return false
 }

 // Get issues a GET to the specified URL.  If the response is one of the following
 // redirect codes, Get follows the redirect, up to a maximum of 10 redirects:
 //
 //    301 (Moved Permanently)
 //    302 (Found)
 //    303 (See Other)
 //    307 (Temporary Redirect)
 //
 // An error is returned if there were too many redirects or if there
 // was an HTTP protocol error. A non-2xx response doesn't cause an
 // error.
 //
 // When err is nil, resp always contains a non-nil resp.Body.
 // Caller should close resp.Body when done reading from it.
 //
 // Get is a wrapper around DefaultClient.Get.
 func Get(url string) (resp *Response, err error) {
 	return DefaultClient.Get(url)
 }

 // Get issues a GET to the specified URL.  If the response is one of the
 // following redirect codes, Get follows the redirect after calling the
 // Client's CheckRedirect function.
 //
 //    301 (Moved Permanently)
 //    302 (Found)
 //    303 (See Other)
 //    307 (Temporary Redirect)
 //
 // An error is returned if the Client's CheckRedirect function fails
 // or if there was an HTTP protocol error. A non-2xx response doesn't
 // cause an error.
 //
 // When err is nil, resp always contains a non-nil resp.Body.
 // Caller should close resp.Body when done reading from it.
 func (c *Client) Get(url string) (resp *Response, err error) {
 	req, err := NewRequest("GET", url, nil)
 	if err != nil {
 		return nil, err
 	}
 	return c.doFollowingRedirects(req, shouldRedirectGet)
 }

 func alwaysFalse() bool { return false }

 func (c *Client) doFollowingRedirects(ireq *Request, shouldRedirect func(int) bool) (resp *Response, err error) {
 	var base *url.URL
 	redirectChecker := c.CheckRedirect
 	if redirectChecker == nil {
 		redirectChecker = defaultCheckRedirect
 	}
 	var via []*Request

 	if ireq.URL == nil {
 		ireq.closeBody()
 		return nil, errors.New("http: nil Request.URL")
 	}

 	var reqmu sync.Mutex // guards req
 	req := ireq

 	var timer *time.Timer
 	var atomicWasCanceled int32 // atomic bool (1 or 0)
 	var wasCanceled = alwaysFalse
 	if c.Timeout > 0 {
 		wasCanceled = func() bool { return atomic.LoadInt32(&atomicWasCanceled) != 0 }
 		type canceler interface {
 			CancelRequest(*Request)
 		}
 		tr, ok := c.transport().(canceler)
 		if !ok {
 			return nil, fmt.Errorf("net/http: Client Transport of type %T doesn't support CancelRequest; Timeout not supported", c.transport())
 		}
 		timer = time.AfterFunc(c.Timeout, func() {
 			atomic.StoreInt32(&atomicWasCanceled, 1)
 			reqmu.Lock()
 			defer reqmu.Unlock()
 			tr.CancelRequest(req)
 		})
 	}

 	urlStr := "" // next relative or absolute URL to fetch (after first request)
 	redirectFailed := false
 	for redirect := 0; ; redirect++ {
 		if redirect != 0 {
 			nreq := new(Request)
 			nreq.Method = ireq.Method
 			if ireq.Method == "POST" || ireq.Method == "PUT" {
 				nreq.Method = "GET"
 			}
 			nreq.Header = make(Header)
 			nreq.URL, err = base.Parse(urlStr)
 			if err != nil {
 				break
 			}
 			if len(via) > 0 {
 				// Add the Referer header.
 				lastReq := via[len(via)-1]
 				if ref := refererForURL(lastReq.URL, nreq.URL); ref != "" {
 					nreq.Header.Set("Referer", ref)
 				}

 				err = redirectChecker(nreq, via)
 				if err != nil {
 					redirectFailed = true
 					break
 				}
 			}
 			reqmu.Lock()
 			req = nreq
 			reqmu.Unlock()
 		}

 		urlStr = req.URL.String()
 		if resp, err = c.send(req); err != nil {
 			if wasCanceled() {
 				err = &httpError{
 					err:     err.Error() + " (Client.Timeout exceeded while awaiting headers)",
 					timeout: true,
 				}
 			}
 			break
 		}

 		if shouldRedirect(resp.StatusCode) {
 			// Read the body if small so underlying TCP connection will be re-used.
 			// No need to check for errors: if it fails, Transport won't reuse it anyway.
 			const maxBodySlurpSize = 2 << 10
 			if resp.ContentLength == -1 || resp.ContentLength <= maxBodySlurpSize {
 				io.CopyN(ioutil.Discard, resp.Body, maxBodySlurpSize)
 			}
 			resp.Body.Close()
 			if urlStr = resp.Header.Get("Location"); urlStr == "" {
 				err = errors.New(fmt.Sprintf("%d response missing Location header", resp.StatusCode))
 				break
 			}
 			base = req.URL
 			via = append(via, req)
 			continue
 		}
 		if timer != nil {
 			resp.Body = &cancelTimerBody{
 				t:              timer,
 				rc:             resp.Body,
 				reqWasCanceled: wasCanceled,
 			}
 		}
 		return resp, nil
 	}

 	method := ireq.Method
 	urlErr := &url.Error{
 		Op:  method[0:1] + strings.ToLower(method[1:]),
 		URL: urlStr,
 		Err: err,
 	}

 	if redirectFailed {
 		// Special case for Go 1 compatibility: return both the response
 		// and an error if the CheckRedirect function failed.
 		// See http://golang.org/issue/3795
 		return resp, urlErr
 	}

 	if resp != nil {
 		resp.Body.Close()
 	}
 	return nil, urlErr
 }

 func defaultCheckRedirect(req *Request, via []*Request) error {
 	if len(via) >= 10 {
 		return errors.New("stopped after 10 redirects")
 	}
 	return nil
 }

 // Post issues a POST to the specified URL.
 //
 // Caller should close resp.Body when done reading from it.
 //
 // Post is a wrapper around DefaultClient.Post
 func Post(url string, bodyType string, body io.Reader) (resp *Response, err error) {
 	return DefaultClient.Post(url, bodyType, body)
 }

 // Post issues a POST to the specified URL.
 //
 // Caller should close resp.Body when done reading from it.
 //
 // If the provided body is also an io.Closer, it is closed after the
 // request.
 func (c *Client) Post(url string, bodyType string, body io.Reader) (resp *Response, err error) {
 	req, err := NewRequest("POST", url, body)
 	if err != nil {
 		return nil, err
 	}
 	req.Header.Set("Content-Type", bodyType)
 	return c.doFollowingRedirects(req, shouldRedirectPost)
 }

 // PostForm issues a POST to the specified URL, with data's keys and
 // values URL-encoded as the request body.
 //
 // When err is nil, resp always contains a non-nil resp.Body.
 // Caller should close resp.Body when done reading from it.
 //
 // PostForm is a wrapper around DefaultClient.PostForm
 func PostForm(url string, data url.Values) (resp *Response, err error) {
 	return DefaultClient.PostForm(url, data)
 }

 // PostForm issues a POST to the specified URL,
 // with data's keys and values urlencoded as the request body.
 //
 // When err is nil, resp always contains a non-nil resp.Body.
 // Caller should close resp.Body when done reading from it.
 func (c *Client) PostForm(url string, data url.Values) (resp *Response, err error) {
 	return c.Post(url, "application/x-www-form-urlencoded", strings.NewReader(data.Encode()))
 }

 // Head issues a HEAD to the specified URL.  If the response is one of the
 // following redirect codes, Head follows the redirect after calling the
 // Client's CheckRedirect function.
 //
 //    301 (Moved Permanently)
 //    302 (Found)
 //    303 (See Other)
 //    307 (Temporary Redirect)
 //
 // Head is a wrapper around DefaultClient.Head
 func Head(url string) (resp *Response, err error) {
 	return DefaultClient.Head(url)
 }

 // Head issues a HEAD to the specified URL.  If the response is one of the
 // following redirect codes, Head follows the redirect after calling the
 // Client's CheckRedirect function.
 //
 //    301 (Moved Permanently)
 //    302 (Found)
 //    303 (See Other)
 //    307 (Temporary Redirect)
 func (c *Client) Head(url string) (resp *Response, err error) {
 	req, err := NewRequest("HEAD", url, nil)
 	if err != nil {
 		return nil, err
 	}
 	return c.doFollowingRedirects(req, shouldRedirectGet)
 }

 // cancelTimerBody is an io.ReadCloser that wraps rc with two features:
 // 1) on Read EOF or Close, the timer t is Stopped,
 // 2) On Read failure, if reqWasCanceled is true, the error is wrapped and
 //    marked as net.Error that hit its timeout.
 type cancelTimerBody struct {
 	t              *time.Timer
 	rc             io.ReadCloser
 	reqWasCanceled func() bool
 }

 func (b *cancelTimerBody) Read(p []byte) (n int, err error) {
 	n, err = b.rc.Read(p)
 	if err == io.EOF {
 		b.t.Stop()
 	} else if err != nil && b.reqWasCanceled() {
 		return n, &httpError{
 			err:     err.Error() + " (Client.Timeout exceeded while reading body)",
 			timeout: true,
 		}
 	}
 	return
 }

 func (b *cancelTimerBody) Close() error {
 	err := b.rc.Close()
 	b.t.Stop()
 	return err
 }
	// Copyright 2009 The Go Authors. All rights reserved.
	// Use of this source code is governed by a BSD-style
	// license that can be found in the LICENSE file.

	// HTTP client. See RFC 2616.
	//
	// This is the high-level Client interface.
	// The low-level implementation is in transport.go.

	package http

	import (
	"encoding/base64"
	"errors"
	"fmt"
	"io"
	"io/ioutil"
	"log"
	"net/url"
	"strings"
	"sync"
	"sync/atomic"
	"time"
	)

	// A Client is an HTTP client. Its zero value (DefaultClient) is a
	// usable client that uses DefaultTransport.
	//
	// The Client's Transport typically has internal state (cached TCP
	// connections), so Clients should be reused instead of created as
	// needed. Clients are safe for concurrent use by multiple goroutines.
	//
	// A Client is higher-level than a RoundTripper (such as Transport)
	// and additionally handles HTTP details such as cookies and
	// redirects.
	type Client struct {
	// Transport specifies the mechanism by which individual
	// HTTP requests are made.
	// If nil, DefaultTransport is used.
	Transport RoundTripper

	// CheckRedirect specifies the policy for handling redirects.
	// If CheckRedirect is not nil, the client calls it before
	// following an HTTP redirect. The arguments req and via are
	// the upcoming request and the requests made already, oldest
	// first. If CheckRedirect returns an error, the Client's Get
	// method returns both the previous Response and
	// CheckRedirect's error (wrapped in a url.Error) instead of
	// issuing the Request req.
	//
	// If CheckRedirect is nil, the Client uses its default policy,
	// which is to stop after 10 consecutive requests.
	CheckRedirect func(req Request, via []Request) error

	// Jar specifies the cookie jar.
	// If Jar is nil, cookies are not sent in requests and ignored
	// in responses.
	Jar CookieJar

	// Timeout specifies a time limit for requests made by this
	// Client. The timeout includes connection time, any
	// redirects, and reading the response body. The timer remains
	// running after Get, Head, Post, or Do return and will
	// interrupt reading of the Response.Body.
	//
	// A Timeout of zero means no timeout.
	//
	// The Client's Transport must support the CancelRequest
	// method or Client will return errors when attempting to make
	// a request with Get, Head, Post, or Do. Client's default
	// Transport (DefaultTransport) supports CancelRequest.
	Timeout time.Duration
	}

	// DefaultClient is the default Client and is used by Get, Head, and Post.
	var DefaultClient = &Client{}

	// RoundTripper is an interface representing the ability to execute a
	// single HTTP transaction, obtaining the Response for a given Request.
	//
	// A RoundTripper must be safe for concurrent use by multiple
	// goroutines.
	type RoundTripper interface {
	// RoundTrip executes a single HTTP transaction, returning
	// the Response for the request req. RoundTrip should not
	// attempt to interpret the response. In particular,
	// RoundTrip must return err == nil if it obtained a response,
	// regardless of the response's HTTP status code. A non-nil
	// err should be reserved for failure to obtain a response.
	// Similarly, RoundTrip should not attempt to handle
	// higher-level protocol details such as redirects,
	// authentication, or cookies.
	//
	// RoundTrip should not modify the request, except for
	// consuming and closing the Body, including on errors. The
	// request's URL and Header fields are guaranteed to be
	// initialized.
	RoundTrip(Request) (Response, error)
	}

	// Given a string of the form "host", "host:port", or "[ipv6::address]:port",
	// return true if the string includes a port.
	func hasPort(s string) bool { return strings.LastIndex(s, ":") > strings.LastIndex(s, "]") }

	// refererForURL returns a referer without any authentication info or
	// an empty string if lastReq scheme is https and newReq scheme is http.
	func refererForURL(lastReq, newReq *url.URL) string {
	// https://tools.ietf.org/html/rfc7231#section-5.5.2
	// "Clients SHOULD NOT include a Referer header field in a
	// (non-secure) HTTP request if the referring page was
	// transferred with a secure protocol."
	if lastReq.Scheme == "https" && newReq.Scheme == "http" {
	return ""
	}
	referer := lastReq.String()
	if lastReq.User != nil {
	// This is not very efficient, but is the best we can
	// do without:
	// - introducing a new method on URL
	// - creating a race condition
	// - copying the URL struct manually, which would cause
	// maintenance problems down the line
	auth := lastReq.User.String() + "@"
	referer = strings.Replace(referer, auth, "", 1)
	}
	return referer
	}

	// Used in Send to implement io.ReadCloser by bundling together the
	// bufio.Reader through which we read the response, and the underlying
	// network connection.
	type readClose struct {
	io.Reader
	io.Closer
	}

	func (c Client) send(req Request) (*Response, error) {
	if c.Jar != nil {
	for _, cookie := range c.Jar.Cookies(req.URL) {
	req.AddCookie(cookie)
	}
	}
	resp, err := send(req, c.transport())
	if err != nil {
	return nil, err
	}
	if c.Jar != nil {
	if rc := resp.Cookies(); len(rc) > 0 {
	c.Jar.SetCookies(req.URL, rc)
	}
	}
	return resp, err
	}

	// Do sends an HTTP request and returns an HTTP response, following
	// policy (e.g. redirects, cookies, auth) as configured on the client.
	//
	// An error is returned if caused by client policy (such as
	// CheckRedirect), or if there was an HTTP protocol error.
	// A non-2xx response doesn't cause an error.
	//
	// When err is nil, resp always contains a non-nil resp.Body.
	//
	// Callers should close resp.Body when done reading from it. If
	// resp.Body is not closed, the Client's underlying RoundTripper
	// (typically Transport) may not be able to re-use a persistent TCP
	// connection to the server for a subsequent "keep-alive" request.
	//
	// The request Body, if non-nil, will be closed by the underlying
	// Transport, even on errors.
	//
	// Generally Get, Post, or PostForm will be used instead of Do.
	func (c Client) Do(req Request) (resp *Response, err error) {
	if req.Method == "GET" \|\| req.Method == "HEAD" {
	return c.doFollowingRedirects(req, shouldRedirectGet)
	}
	if req.Method == "POST" \|\| req.Method == "PUT" {
	return c.doFollowingRedirects(req, shouldRedirectPost)
	}
	return c.send(req)
	}

	func (c *Client) transport() RoundTripper {
	if c.Transport != nil {
	return c.Transport
	}
	return DefaultTransport
	}

	// send issues an HTTP request.
	// Caller should close resp.Body when done reading from it.
	func send(req Request, t RoundTripper) (resp Response, err error) {
	if t == nil {
	req.closeBody()
	return nil, errors.New("http: no Client.Transport or DefaultTransport")
	}

	if req.URL == nil {
	req.closeBody()
	return nil, errors.New("http: nil Request.URL")
	}

	if req.RequestURI != "" {
	req.closeBody()
	return nil, errors.New("http: Request.RequestURI can't be set in client requests.")
	}

	// Most the callers of send (Get, Post, et al) don't need
	// Headers, leaving it uninitialized. We guarantee to the
	// Transport that this has been initialized, though.
	if req.Header == nil {
	req.Header = make(Header)
	}

	if u := req.URL.User; u != nil {
	username := u.Username()
	password, _ := u.Password()
	req.Header.Set("Authorization", "Basic "+basicAuth(username, password))
	}
	resp, err = t.RoundTrip(req)
	if err != nil {
	if resp != nil {
	log.Printf("RoundTripper returned a response & error; ignoring response")
	}
	return nil, err
	}
	return resp, nil
	}

	// See 2 (end of page 4) http://www.ietf.org/rfc/rfc2617.txt
	// "To receive authorization, the client sends the userid and password,
	// separated by a single colon (":") character, within a base64
	// encoded string in the credentials."
	// It is not meant to be urlencoded.
	func basicAuth(username, password string) string {
	auth := username + ":" + password
	return base64.StdEncoding.EncodeToString([]byte(auth))
	}

	// True if the specified HTTP status code is one for which the Get utility should
	// automatically redirect.
	func shouldRedirectGet(statusCode int) bool {
	switch statusCode {
	case StatusMovedPermanently, StatusFound, StatusSeeOther, StatusTemporaryRedirect:
	return true
	}
	return false
	}

	// True if the specified HTTP status code is one for which the Post utility should
	// automatically redirect.
	func shouldRedirectPost(statusCode int) bool {
	switch statusCode {
	case StatusFound, StatusSeeOther:
	return true
	}
	return false
	}

	// Get issues a GET to the specified URL. If the response is one of the following
	// redirect codes, Get follows the redirect, up to a maximum of 10 redirects:
	//
	// 301 (Moved Permanently)
	// 302 (Found)
	// 303 (See Other)
	// 307 (Temporary Redirect)
	//
	// An error is returned if there were too many redirects or if there
	// was an HTTP protocol error. A non-2xx response doesn't cause an
	// error.
	//
	// When err is nil, resp always contains a non-nil resp.Body.
	// Caller should close resp.Body when done reading from it.
	//
	// Get is a wrapper around DefaultClient.Get.
	func Get(url string) (resp *Response, err error) {
	return DefaultClient.Get(url)
	}

	// Get issues a GET to the specified URL. If the response is one of the
	// following redirect codes, Get follows the redirect after calling the
	// Client's CheckRedirect function.
	//
	// 301 (Moved Permanently)
	// 302 (Found)
	// 303 (See Other)
	// 307 (Temporary Redirect)
	//
	// An error is returned if the Client's CheckRedirect function fails
	// or if there was an HTTP protocol error. A non-2xx response doesn't
	// cause an error.
	//
	// When err is nil, resp always contains a non-nil resp.Body.
	// Caller should close resp.Body when done reading from it.
	func (c Client) Get(url string) (resp Response, err error) {
	req, err := NewRequest("GET", url, nil)
	if err != nil {
	return nil, err
	}
	return c.doFollowingRedirects(req, shouldRedirectGet)
	}

	func alwaysFalse() bool { return false }

	func (c Client) doFollowingRedirects(ireq Request, shouldRedirect func(int) bool) (resp *Response, err error) {
	var base *url.URL
	redirectChecker := c.CheckRedirect
	if redirectChecker == nil {
	redirectChecker = defaultCheckRedirect
	}
	var via []*Request

	if ireq.URL == nil {
	ireq.closeBody()
	return nil, errors.New("http: nil Request.URL")
	}

	var reqmu sync.Mutex // guards req
	req := ireq

	var timer *time.Timer
	var atomicWasCanceled int32 // atomic bool (1 or 0)
	var wasCanceled = alwaysFalse
	if c.Timeout > 0 {
	wasCanceled = func() bool { return atomic.LoadInt32(&atomicWasCanceled) != 0 }
	type canceler interface {
	CancelRequest(*Request)
	}
	tr, ok := c.transport().(canceler)
	if !ok {
	return nil, fmt.Errorf("net/http: Client Transport of type %T doesn't support CancelRequest; Timeout not supported", c.transport())
	}
	timer = time.AfterFunc(c.Timeout, func() {
	atomic.StoreInt32(&atomicWasCanceled, 1)
	reqmu.Lock()
	defer reqmu.Unlock()
	tr.CancelRequest(req)
	})
	}

	urlStr := "" // next relative or absolute URL to fetch (after first request)
	redirectFailed := false
	for redirect := 0; ; redirect++ {
	if redirect != 0 {
	nreq := new(Request)
	nreq.Method = ireq.Method
	if ireq.Method == "POST" \|\| ireq.Method == "PUT" {
	nreq.Method = "GET"
	}
	nreq.Header = make(Header)
	nreq.URL, err = base.Parse(urlStr)
	if err != nil {
	break
	}
	if len(via) > 0 {
	// Add the Referer header.
	lastReq := via[len(via)-1]
	if ref := refererForURL(lastReq.URL, nreq.URL); ref != "" {
	nreq.Header.Set("Referer", ref)
	}

	err = redirectChecker(nreq, via)
	if err != nil {
	redirectFailed = true
	break
	}
	}
	reqmu.Lock()
	req = nreq
	reqmu.Unlock()
	}

	urlStr = req.URL.String()
	if resp, err = c.send(req); err != nil {
	if wasCanceled() {
	err = &httpError{
	err: err.Error() + " (Client.Timeout exceeded while awaiting headers)",
	timeout: true,
	}
	}
	break
	}

	if shouldRedirect(resp.StatusCode) {
	// Read the body if small so underlying TCP connection will be re-used.
	// No need to check for errors: if it fails, Transport won't reuse it anyway.
	const maxBodySlurpSize = 2 << 10
	if resp.ContentLength == -1 \|\| resp.ContentLength <= maxBodySlurpSize {
	io.CopyN(ioutil.Discard, resp.Body, maxBodySlurpSize)
	}
	resp.Body.Close()
	if urlStr = resp.Header.Get("Location"); urlStr == "" {
	err = errors.New(fmt.Sprintf("%d response missing Location header", resp.StatusCode))
	break
	}
	base = req.URL
	via = append(via, req)
	continue
	}
	if timer != nil {
	resp.Body = &cancelTimerBody{
	t: timer,
	rc: resp.Body,
	reqWasCanceled: wasCanceled,
	}
	}
	return resp, nil
	}

	method := ireq.Method
	urlErr := &url.Error{
	Op: method[0:1] + strings.ToLower(method[1:]),
	URL: urlStr,
	Err: err,
	}

	if redirectFailed {
	// Special case for Go 1 compatibility: return both the response
	// and an error if the CheckRedirect function failed.
	// See http://golang.org/issue/3795
	return resp, urlErr
	}

	if resp != nil {
	resp.Body.Close()
	}
	return nil, urlErr
	}

	func defaultCheckRedirect(req Request, via []Request) error {
	if len(via) >= 10 {
	return errors.New("stopped after 10 redirects")
	}
	return nil
	}

	// Post issues a POST to the specified URL.
	//
	// Caller should close resp.Body when done reading from it.
	//
	// Post is a wrapper around DefaultClient.Post
	func Post(url string, bodyType string, body io.Reader) (resp *Response, err error) {
	return DefaultClient.Post(url, bodyType, body)
	}

	// Post issues a POST to the specified URL.
	//
	// Caller should close resp.Body when done reading from it.
	//
	// If the provided body is also an io.Closer, it is closed after the
	// request.
	func (c Client) Post(url string, bodyType string, body io.Reader) (resp Response, err error) {
	req, err := NewRequest("POST", url, body)
	if err != nil {
	return nil, err
	}
	req.Header.Set("Content-Type", bodyType)
	return c.doFollowingRedirects(req, shouldRedirectPost)
	}

	// PostForm issues a POST to the specified URL, with data's keys and
	// values URL-encoded as the request body.
	//
	// When err is nil, resp always contains a non-nil resp.Body.
	// Caller should close resp.Body when done reading from it.
	//
	// PostForm is a wrapper around DefaultClient.PostForm
	func PostForm(url string, data url.Values) (resp *Response, err error) {
	return DefaultClient.PostForm(url, data)
	}

	// PostForm issues a POST to the specified URL,
	// with data's keys and values urlencoded as the request body.
	//
	// When err is nil, resp always contains a non-nil resp.Body.
	// Caller should close resp.Body when done reading from it.
	func (c Client) PostForm(url string, data url.Values) (resp Response, err error) {
	return c.Post(url, "application/x-www-form-urlencoded", strings.NewReader(data.Encode()))
	}

	// Head issues a HEAD to the specified URL. If the response is one of the
	// following redirect codes, Head follows the redirect after calling the
	// Client's CheckRedirect function.
	//
	// 301 (Moved Permanently)
	// 302 (Found)
	// 303 (See Other)
	// 307 (Temporary Redirect)
	//
	// Head is a wrapper around DefaultClient.Head
	func Head(url string) (resp *Response, err error) {
	return DefaultClient.Head(url)
	}

	// Head issues a HEAD to the specified URL. If the response is one of the
	// following redirect codes, Head follows the redirect after calling the
	// Client's CheckRedirect function.
	//
	// 301 (Moved Permanently)
	// 302 (Found)
	// 303 (See Other)
	// 307 (Temporary Redirect)
	func (c Client) Head(url string) (resp Response, err error) {
	req, err := NewRequest("HEAD", url, nil)
	if err != nil {
	return nil, err
	}
	return c.doFollowingRedirects(req, shouldRedirectGet)
	}

	// cancelTimerBody is an io.ReadCloser that wraps rc with two features:
	// 1) on Read EOF or Close, the timer t is Stopped,
	// 2) On Read failure, if reqWasCanceled is true, the error is wrapped and
	// marked as net.Error that hit its timeout.
	type cancelTimerBody struct {
	t *time.Timer
	rc io.ReadCloser
	reqWasCanceled func() bool
	}

	func (b *cancelTimerBody) Read(p []byte) (n int, err error) {
	n, err = b.rc.Read(p)
	if err == io.EOF {
	b.t.Stop()
	} else if err != nil && b.reqWasCanceled() {
	return n, &httpError{
	err: err.Error() + " (Client.Timeout exceeded while reading body)",
	timeout: true,
	}
	}
	return
	}

	func (b *cancelTimerBody) Close() error {
	err := b.rc.Close()
	b.t.Stop()
	return err
	}